First-principles study of the structural and thermoelectric properties of Y-doped α-SrSi 2

The narrow-gap semiconductor alpha-SrSi2 is a promising candidate for low-temperature thermoelectric applications with low environmental load. The only experimental report in which alpha-SrSi2 is reported to have n-type conductivity is one where it had been doped with yttrium. To further clarify the effects of impurities, theoretical studies are needed. The alpha-SrSi2 has a very narrow band gap (similar to 13-35 meV), causing difficulties in the accurate calculation of the electronic and thermoelectric properties. In our previous study, we overcame this problem for undoped alpha-SrSi2 using hybrid functional theory. We used this method in this study to investigate the structures, energetic stabilities, electronic structures, and thermoelectric properties of Y-doped alpha-SrSi2. The results indicate that substitution at Sr-sites is energetically about two times more stable than that at Si-sites. Furthermore, negative Seebeck coefficients were obtained at low temperatures and reverted to p-type with increasing temperature, which is consistent with the experimental results.